Method of manufacturing a flexure suspension assembly

ABSTRACT

A method of manufacturing a flexure suspension assembly which includes forming four quadrantally and radially disposed single axis flexure joints in a first cylindrical member and four quadrantally and radially disposed single axis flexure joints in a second cylindrical member. The longitudinal axes of the flexure joints in the first cylindrical member are substantially parallel to the longitudinal cylinder axis which is coincident with the spin axis of the suspension assembly and the longitudinal axes of the joints in the second cylindrical member are substantially perpendicular to the longitudinal axis of the second member. The first and second members are integrally joined together in concentric relationship with the bending axes of the four joints in each cylinder in radial alignment to form a composite cylindrical member. The composite cylindrical member is then separated by electro discharge machining into the foregoing components of the flexure suspension assembly.

This is a division, of application Ser. No. 686,127 filed May 13, 1976,U.S. Pat. No. 4,100,813.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to flexure suspension assemblies for inertialdevices such as gyroscopes and the like and more particularly to aflexure suspension assembly having two degrees of angular rotationalfreedom and to a method of making the same.

2. Description of the Prior Art

Certain types of gyroscopes and other inertial sensing devices employ aflexure suspension assembly to connect a rotatable spin shaft to aflywheel or inertial member so that the flywheel or inertial member maybe brought up to a suitably high speed by rotation of the spin shaft.The spin shaft is fixedly mounted against angular rotation but theflywheel of the gyroscope or other inertial device must be free to"precess" or angularly rotate about two precession axes which areorthogonally related to the spin axis of the spin shaft. Accordingly,the flexure suspension assembly must be rotatable about the spin axisand must have two degrees of angular rotational freedom about the twoprecession axes. The suspension assembly must also provide adequateaxial structural support for the flywheel, since the weight of theflywheel is ultimately borne by the spin shaft. When the spin shaft isrotated to bring the flywheel to full spin speed, the suspensionassembly must provide the required radial support. Accordingly, theflexure suspension assembly provides both axial and radial support forrotation of the flywheel. The support provided must prevent translatorymovement of the flywheel with respect to the spin shaft along the spinaxis and the two orthogonally related precession axes when the gyroscopeor other inertial device is subjected to external acceleration forcesalong these axes. The foregoing structural support must be provided,however, without imposing substantial flexural restraints on the angularrotation of the flywheel about the two precession axes or error torqueswill be produced during gyroscope operation which will degrade theaccuracy of the gyroscope output information.

Flexure suspension assemblies have been produced by a number ofdifferent methods which utilize the formation of single axis flexurejoints. Single axis flexure joints are essentially thin sections ofmetal or other suitable material of which the suspension assembly ismade which may be bent or flexed about only a single axis. A single axisflexure joint may be formed by drilling or otherwise forming a pair ofclosely spaced parallel holes in a member and separating the member intotwo portions which are joined only by the thin section of materialbetween the closely spaced holes. This will produce a flexure jointwhich may be bent or flexed about a single bending axis which is midwaybetween the holes and is parallel to the two longitudinal axes of theholes. The longitudinal axis of the flexure joint would then beperpendicular to the bending axis and would be located equidistantlybetween the two holes.

A known method of producing a flexure suspension assembly having singleaxis flexure joints involves the use of a single cylindrical member inwhich four single axis flexure joints are distributed about theperiphery of the member at 90° intervals by the boring of four pairs ofclosely spaced and radially separated holes. The longitudinal axes ofthese flexure joints are substantially parallel to the longitudinal axisof the cylinder and the bending axes are radially disposed. The singlecylinder is then separated by known techniques into spin shaft andflywheel mounting members and gimbal members which are interconnected byeight single axis flexure joints all having their longitudinal axesparallel to the longitudinal cylinder axis. In the resulting flexuresuspension assembly, the flywheel is supported radially by four of theaxially-extending flexure joints loaded in shear. Axial support for theflywheel is provided by all of the eight axial flexure joints loaded intension. Although the resulting suspension assembly provides good axialsupport for the flywheel, it has the disadvantage of providing poorradial support. In order to increase the radial support provided by thistype of suspension assembly, the single axis flexure joints must be madestronger. However, the strengthening of the flexure joints alsoincreases the stiffness of the joints and increases the flexuralrestraints imposed by the suspension assembly upon the flywheel forangular rotation about the gyroscope precession axes. Although the errortorques resulting from the increased flexural restraints could beminimized by adjusting or tuning the moments of inertia of the gimbalmembers of the assembly, the tuning is made very difficult by theincreased stiffness of the flexure joints.

Other methods of making flexure suspension assemblies involve the use oftwo separate cylindrical members which are individually separated ormachined into the requisite number of flexure joints and other componentparts of the flexure suspension assembly prior to joining. After eachcylindrical member has been separated into its share of the componentparts of the assembly, the machined members are joined together at theflexure joints produced in each member to provide the final flexuresuspension assembly. This method also produces a suspension assemblywhich suffers from the structural disadvantages of the assembliesproduced by the single cylinder method. Additionally, the known methodsand suspension assemblies utilize a technique for mounting the flexuresuspension assembly on the gyroscope spin shaft wherein a connectingshaft is formed or machined as a part of the spin shaft mounting member.The connecting shaft is then blind cemented into a recess in thegyroscope spin shaft. With this arrangement, the distribution of theflywheel inertial load is no longer centrally located at the shaftmounting surface but is instead cantilevered away from the cement jointmounting surface. This may produce a source of gyroscope drift errorswhich would not exist if the flexure suspension assembly could becentrally mounted on the gyroscope spin shaft with the flywheel inertialload evenly supported at the shaft mounting surface.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a flexure suspensionassembly for coupling the rotatable spin shaft and flywheel of inertialdevices and the like which exhibits a high degree of structural strengthand provides good axial and radial support for the flywheel.

It is a further object of this invention to provide a flexure suspensionassembly for inertial devices and the like wherein good radial and axialsupport are provided for the flywheel of the device without theimposition of substantial flexural restraints on the operation of theinertial device.

It is a still further object of this invention to provide a flexuresuspension assembly which includes means for tuning the moments ofinertial of the gimbal members of the assembly.

It is another object of this invention to provide a flexure suspensionassembly which is mechanically rugged in construction, imposes lowflexural restraints and may be fabricated by an easily practiced methodof making the same.

It is an additional object of this invention to provide a flexuresuspension assembly for coupling the spin shaft and flywheel of inertialdevices and the like which permits central mounting of the flexuresuspension assembly to the inertial device spin shaft, so that theinertial load is evenly supported by the shaft mounting surface.

It is still another object of this invention to provide a method ofmaking two degree of angular rotational freedom flexure suspensionassemblies which is easily practiced and which produces a flexuresuspension assembly having superior structural strength and operationalcharacteristics.

It is an additional object of this invention to provide a method ofmaking two degree of freedom flexure suspension assemblies in which twocylinders are utilized but all separational work is carried out afterthe two cylinders are joined, so that delicate component parts need notbe handled prior to joining and are protected from mishandling.

Briefly, the flexure suspension assembly of the invention comprisesfirst mounting means adapted to be coupled to the inertial device spinshaft for rotation therewith about the spin axis and first gimbal meanscoupled by first single axis flexure joint means to the first mountingmeans for rotation therewith about the spin axis. The longitudinal axisof said first flexure joint means is substantially parallel to the spinaxis and the bending axis thereof is aligned with one of the precessionaxes to permit relative angular rotation between the first gimbal meansand the first mounting means about said one precession axis. Secondsingle axis flexure joint means couple second gimbal means to said firstmounting means for rotation therewith about the spin axis. Thelongitudinal axis of the second flexure joint means is substantiallyparallel to the spin axis and the bending axis is aligned with the otherof said precession axes to permit relative angular rotation between thesecond gimbal means and the first mounting means about said otherprecession axis. The assembly also comprises second mounting meansadapted to be coupled to the inertial device flywheel. Third single axisflexure joint means having the longitudinal axis thereof substantiallyperpendicular to the spin axis and the bending axis thereof aligned withsaid other precession axis couple the second mounting means to the firstgimbal means and fourth single axis flexure joint means having thelongitudinal axis thereof substantially perpendicular to the spin axisand the bending axis thereof aligned with said one precession axiscouple the second mounting means to the second gimbal means, whereby thefirst and second mounting means are coupled for rotation together aboutthe spin axis and for relative angular rotation therebetween about bothof the precession axes. Means mounted on each of the first and secondgimbal means may also be provided to adjust the moment of inertia of thegimbal means.

The invention also contemplates a method of making the foregoing flexuresuspension assembly which has two degrees of angular rotational freedomabout first and second axes which are perpendicular to each other and toa reference axis. The method comprises the steps of making first andsecond pairs of radially disposed single axis flexure joints in a firstcylindrical member and third and fourth pairs of radially disposedsingle axis flexure joints in a second cylindrical member having acentral concentrically disposed aperture therein adapted to receive thefirst member. The flexure joints of each of said first and second pairsare disposed on opposite sides of the first member and have the bendingaxes thereof in axial alignment and the longitudinal axes thereofsubstantially parallel to the longitudinal axis of said first member.The bending axes of the first and second pairs of joints areorthogonally related to the longitudinal axis of the first member. Theflexure joints of each of the third and fourth pairs are disposed onopposite sides of the central aperture in the second member and have thebending axes thereof in axial alignment and the longitudinal axesthereof substantially perpendicular to the longitudinal axis of thesecond member. The bending axes of the third and fourth pairs of jointsare orthogonally related to the longitudinal axis of the second member.The next step comprises joining the first member to the second memberwith the first member concentrically disposed in the central aperture ofthe second member to form a cylindrical, integrally-connected compositemember having a longitudinal axis coincident with the reference axis andthe bending axes of the first and fourth pairs of flexure jointscoincident with the first axis and the bending axes of the second andthird pairs of flexure joints coincident with the second axis. Finally,the cylindrical composite member is separated into a cylindrical innermounting member having a longitudinal axis thereof coincident with thereference axis, an annular outer mounting member concentrically disposedabout the inner mounting member and separated therefrom by an annularsection of the composite member, a first gimbal member comprising afirst segment of the composite member annular section coupled by thefirst pair of flexure joints to the inner mounting member and by thethird pair of flexure joints to the outer mounting member, and a secondgimbal member comprising a second segment of the composite memberannular section coupled by the second pair of flexure joints to theinner mounting member and by the fourth pair of flexure joints to theouter mounting member, so that relative angular rotation between theinner and outer mounting members is permitted about said first andsecond axes. Each flexure joint of the first and second pairs or flexurejoints may be made by boring a pair of radially disposed, closely spacedand radially separated holes in the first cylindrical member while eachflexure joint of the third and fourth pairs of flexure joints may bemade by boring a pair of radially disposed, closely spaced and radiallyaligned holes in the second cylindrical member.

The nature of the invention and other objects and additional advantagesthereof will be more readily understood by those skilled in the artafter consideration of the following detailed description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view showing the two cylindrical members used inthe method of the invention prior to being joined;

FIG. 2 is a perspective view of a single axis flexure joint of the typeused in the method and apparatus of the invention;

FIG. 3 is a top plan view of the two cylindrical members shown in FIG. 1of the drawings after joining into a composite member and afterseparation of the composite member into the component parts of theflexure suspension assembly of the invention has been completed;

FIG. 4 is an exploded perspective view showing the flexure suspensionassembly of the invention after separation of the composite member hasbeen completed and with the individual components broken apart of theeight flexure joints for convenience of illustration; and

FIG. 5 is a perspective view of a threaded balance weight which may beused with the gimbal members to tune the moments of inertia thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

The flexure suspension assembly of the invention will first be describedby reference to the method of making the same. As seen in FIG. 1 of thedrawings, the method of the invention utilizes a first cylindricalmember 10 and a second cylindrical member 11. Each member is formed of amaterial having suitable mechanical characteristics for flexuresuspension assemblies, such as a high yield steel, for example. Thecylindrical member 10 is adapted to be concentrically disposed in acentrally located cylindrical aperture 12 which extends along thelongitudinal axis Z of the member 11. The member 10 is also providedwith a centrally disposed cylindrical aperture 13 which extends alongthe longitudinal axis Z of that member for convenience in forming theflexure joints. Member 10 has a first pair of single axis flexure joints14A and 14B which are disposed on opposite sides of the member and whichhave their longitudinal axes parallel to the Z axis and their bendingaxes aligned with each other and coincident with the X axis. A secondpair of single axis flexure joints 15A and 15B are disposed on oppositesides of the first member 10 and have their longitudinal axessubstantially parallel to the Z axis and their bending axes coincidentwith the Y axis. The X and Y axes are orthogonally related to the Z axisas illustrated in the drawings. Accordingly, the four flexure joints arequadrantally disposed at 90° intervals around the periphery of thecylindrical member 10 and the bending axis of each joint is radiallyaligned with either the X or the Y axis. Each of the first and secondpairs of flexure joints is formed by boring a pair of radially disposed,closely spaced and radially separated holes 16 in the cylindrical member10, so that the four flexure joints are formed by boring eight of theholes 16. The term "boring" as used herein shall be deemed to meandrilling or grinding or any other suitable method of making the closelyspaced holes which form the flexure joints. The central aperture 13 inthe member 10 will facilitate the boring operation by decreasing theamount of metal or other material to be removed. The longitudinal orcylindrical axes of each pair of the radially separated holes 16 arespaced equidistant from and are parallel to one or the other of the Xand Y axes, so that the bending axis of each joint is coincident witheither the X or Y axis.

The operation of a single axis flexure joint may best be understood byreference to FIG. 2 of the drawings which shows a pair of closely spacedcylindrical holes 17 formed in a block 18 of suitable material. Thelongitudinal axes of the holes 17 lie in a plane defined by the A and Baxes shown in the drawing and are parallel to and spaced equidistantfrom the B axis. The two holes 17 essentially divide the block into afirst portion 18A and a second portion 18B which are joined together bya pair of outer legs 19 and a thin inner leg or section 20. When theouter legs 19 are broken as shown in the drawing, the portions 18A and18B of the block are joined only by the thin section 20 which has alongitudinal axis L which is orthogonally related to the A and B axes.Since the cross sectional area of the thin section 20 is the smallestalong the B axis where the holes are closest together, it is apparentthat this is the bending axis of the section and that the portions 18Aand 18B of the block may be rotated with respect to each other about theB axis. It is also apparent that the portions 18A and 18B of the blockmay not be rotated with respect to each other about either the A or Laxes, so that the flexure joint formed by the section 20 is a singleaxis flexure joint having only one bending axis B which is perpendicularto both the longitudinal axis L of the joint and the axis of alignment Aof the holes 17. The flexibility or stiffness of this type of joint willdepend upon how closely the holes 17 are spaced from each other and uponthe physical characteristics of the material of which the block 18 ismade.

Referring again to FIG. 1 of the drawings, it is seen that a third pairof single axis flexure joints 21A and 21B are formed in the secondcylindrical member 11. The flexure joints of this pair are disposed onopposite sides of the central aperture 12 of the member 11 and havetheir bending axes aligned and coincident with the Y axis. Thelongitudinal axes of these joints, however, are substantiallyperpendicular to the longitudinal axis Z of the cylindrical member 11.In a similar fashion, a fourth pair of single axis flexure joints 22Aand 22B are also formed in the member 11 and have their bending axesaligned and coincident with the X axis and their longitudinal axessubstantially perpendicular to the longitudinal axis Z of the member 11.The four flexure joints of the third and fourth pairs are each made byboring a pair of radially disposed, closely spaced and radially alignedholes 23 in the member 11, so that the longitudinal axes of theseflexure joints are all substantially perpendicular to the longitudinalaxis Z of the member. For reasons which will be explained hereinafter,four axially disposed and quadrantally located threaded holes 24 arealso formed in the cylindrical member 11.

The next step in the method of the invention is the joining together inconcentric relationship of the cylindrical members 10 and 11. The member10 is concentrically disposed in the aperture 12 in member 11 with thebending axes of the first pair of flexure joints 14A and 14B and thefourth pair of flexure joints 22A and 22B in radial alignment andcoincident with the X axis of member 11 and with the bending axes of thesecond pair of flexure joints 15A and 15B and the third pair of flexurejoints 21A and 21B radially aligned and coincident with the Y axis ofmember 11. The joining together of the cylindrical members 10 and 11produces a cylindrical, integrally-connected, composite member having alongitudinal axis Z. The cylinders may be joined by means, such ascementing or welding, for example, and the terms "joining" or "joined"as used herein shall be deemed to include cementing, welding or anyother suitable method of forming an integral composite member. Thecomposite cylindrical member which results from the joining operation isthen separated into the separate flexure joints and other componentparts of the flexure suspension assembly of the invention. Theseparation operation is usually carried out by a method known as electrodischarge machining because of the complex nature of the cuts which mustbe made in the composite cylindrical member. This method of separationinvolves immersing the composite member in an electrolyte bath andutilizing cutting electrodes of various shapes to produce the requiredconfiguration of cuts. Since this method of separation is well known inthe art, it will not be described further herein. However, the terms"separation" or "separating" as used herein shall be deemed to includenot only electro discharge machining but also other types of cutting ormachining operations which are capable of producing the component partsof the assembly shown herein.

The flexure suspension assembly of the invention after separation of thecylindrical composite member formed by cylinders 10 and 11 has beenaccomplished is shown in FIGS. 3 and 4 of the drawings wherein referencenumeral 25 designates the seam between the joined cylindrical members 10and 11. In the exploded perspective view of the assembly shown in FIG. 4of the drawings, the component parts of the assembly are illustrated asbeing broken apart at the eight single axis flexure joints whichinterconnect the component parts in the actual assembly. As seen inFIGS. 3 and 4, the separation operation produces a cylindrical inner orcentral mounting member 26 which is elongated and has the longitudinalaxis thereof coincident with the Z axis of the composite member formedby the joining of members 10 and 11. The inner mounting member 26 isadapted to be coupled to the rotatable spin shaft (not shown) of agyroscope or other inertial device by means such as cementing orwelding, for example, so that the inner mounting member will rotate withthe spin shaft about the spin axis thereof. The spin shaft spin axiswill therefore coincide with the Z axis shown in the drawings. Theseparation operation also produces an outer or closed mounting member 27which is annular in shape and which comprises the outer peripheralportion of the composite cylinder from which it is derived. The annularouter member 27 is adapted to be coupled by cementing, welding or othersuitable means to the flywheel (not shown) of the gyroscope or otherinertial device. The outer mounting member 27 is concentrically disposedabout the inner mounting member 26 and is spaced therefrom by an annularsection or annulus of the composite cylindrical member. The separationoperation divides the annular section or annulus into two segmentscomprising a first gimbal member 28 and a second gimbal member 29 whichare substantially identical in shape and size.

Gimbal member 28 is a bifurcated member having two,substantially-parallel arm portions 30 and 31 which are disposed onopposite sides of the inner mounting member 26 and which areinterconnected at one end of the arm portions by a central portion 32 inwhich is located two of the threaded apertures 24 which were formed inthe cylindrical member 11. The central portion 32 is also provided witha centrally disposed elongated slot 33 which is adapted to receive oneend 34 of the inner mounting member 26. The first gimbal member 28 iscoupled by the first pair of single axis flexure joints 14A and 14B tothe inner mounting member 26 and by the third pair of flexure joints 21Aand 21B to the outer mounting member 27. Flexure joint 14A is formed bya radially extending projection 35 on one side of the slot 33 in thegimbal member central portion 32 and by a radially extending projection36 formed on one side of the other end 37 of the inner mounting member26. Flexure joint 14B is formed by a radial projection 38 on the otherside of the slot 33 and by a radial projection 39 on the other side ofthe mounting member 26 at the end 37 thereof. Since the bending axis ofthe first pair of single axis flexure joints 14A and 14B is coincidentwith the X axis and since the joints are disposed on opposite sides ofthe central mounting member 26, gimbal member 28 may be angularlyrotated with respect to inner mounting member 26 about the X axis andwill rotate or spin with the inner mounting member about the Z spin axiswhen the inner mounting member is connected to the gyroscope spin shaft.The arm portion 31 of gimbal member 28 is cut away at 40 so that aradially extending projection 41 is formed on the inner surface 42 ofthe outer mounting member 27. The projection 41 serves as one half offlexure joint 21A. The remaining half of flexure 21A is an integral partof the arm portion 31 of gimbal member 28. In a similar fashion, oneportion of flexure joint 21B is formed as an integral part of gimbalmember arm portion 30 and the other portion of the joint is formed by aradially extending projection 43 on the inner surface 42 of the outermounting member 27, so that the third pair of flexure joints 21A and 21Bare disposed on opposite sides of the annulus formed by the gimbalmembers 28 and 29. This provides both radial and axial support for theouter mounting member and causes the outer mounting member to rotatewith the gimbal member 28 and the inner mounting member 26 about the Zspin axis. Since the bending axis of the third pair of joints 21A and21B is coincident with the Y axis, the outer mounting member 27 may beangularly rotated about the Y axis with respect to the gimbal member 28.

Gimbal member 29 is substantially identical to gimbal member 28 and hasa pair of substantially parallel arm portions 44 and 45 which areinterconnected at one end thereof by a central portion 46. The gimbalmember central portion 46, however, is located at the opposite end 37 ofthe inner mounting member 26 and is substantially perpendicular to thecentral portion 32 of gimbal member 28, so that when the gimbal members28 and 29 are interleaved the arm portions 30, 31, 44 and 45 of thegimbals are quadrantally disposed about the spin axis Z and the centralmounting member 26. The central portion 46 of gimbal member member 29 isprovided with an elongated slot 47 which is oriented perpendicularly tothe slot 33 in gimbal member 28, so that the slot 47 will receive theend 37 of the inner mounting member 26 and the radial projections 36 and39 formed thereon and will permit gimbal member 29 to be rotated aboutthe Y axis with respect to the inner mounting member 26. The secondgimbal member 29 is connected by the second pair of single axis flexurejoints 15A and 15B to the inner mounting member 26 and by the fourthpair of flexure joints 22A and 22B to the outer mounting member 27.Flexure joint 15A of the second pair is formed by a radially extendingprojection 48 on one side of the central portion 46 of gimbal member 29and by a radially extending projection 49 on one side of inner mountingmember 26 at the end 34 thereof. Flexure joint 15B is formed by aradially extending projection 50 on the opposite side of gimbal membercentral portion 46 and by a radially extending projection 51 on theother side of the inner mounting member 26 at the end 34 thereof, sothat the flexure joints of the second pair are disposed on oppositesides of the inner mounting member and will cause the gimbal member 29to rotate or spin with the inner mounting member about the spin axis Z.Since the bending axis of the second pair of joints 15A and 15B iscoincident with the Y axis, the gimbal member 29 may be angularlyrotated with respect to the inner mounting member 26 about the Y axis.Flexure joint 22A has one portion thereof formed by the gimbal memberarm portion 44 and the other portion thereof formed by a radiallyextending projection 52 formed on the inner surface 42 of the outermounting member 27. Flexure joint 22B is similarly formed by the gimbalmember arm portion 45 and a radially extending projection 53 formed onthe outer mounting member, so that the flexure joints of the fourth pairare disposed on opposite sides of the annulus formed by gimbal members28 and 29 and the outer mounting member 27 will rotate about the spinaxis Z with gimbal member 29 and the spin shaft mounting member 26.Since the bending axis of the fourth pair of flexure joints 22A and 22Bis coincident with the X axis, outer mounting member 27 may be angularlyrotated with respect to the second gimbal member 29 about the X axis.

The operation of the flexure suspension assembly of the invention maybest be seen in FIG. 4 of the drawings wherein the Z axis is the spinaxis for the gryoscope spin shaft and the two orthogonally related X andY axes are the precession axes about which the flywheel must angularlyrotate with respect to the Z axis of the spin shaft. From the foregoingdescription, it is believed apparent that the interleaved gimbal members28 and 29 are oppositely disposed, substantially identical segments ofan annulus concentrically disposed about the inner mounting member 26and the spin axis Z. Since the gimbal members 28 and 29 are coupled tothe inner mounting member 26 by the first pair of flexure joints 14A and14B and the second pair of flexure joints 15A and 15B, both gimbalmembers will rotate about the spin axis with the inner mounting memberwhen the gyroscope spin shaft is rotated. Since the gimbal members 28and 29 are also coupled to the outer mounting member 27 by the thirdpair of flexure joints 21A and 21B and the fourth pair of joints 22A and22B, the outer or flywheel mounting member will also be rotated aboutthe spin axis Z as the gyroscope spin shaft is rotated about that axis.When the gyroscope flywheel precesses about the X precession axis, theouter mounting member 27 will rotate about the X axis and will carrywith it gimbal member 28 because of the rigid connection between gimbalmember 28 and the outer mounting member provided by the third pair offlexure joints 21A and 21B and because of the alignment of the bendingaxis of the first pair of joints 14A and 14B with the X axis. Gimbalmember 29, however, will remain stationary because the bending axis ofthe second pair of joints 15A and 15B is perpendicular to the X axis.The outer mounting member 27 will, however, be free to rotate about theX axis with respect to the fixed gimbal member 29 because the bendingaxis of the fourth pair of flexure joints 22A and 22B is coincident withthe X axis. When the flywheel of the gyroscope precesses about the Yaxis, it will carry with it gimbal member 29 because of the rigidconnection between these members afforded by the fourth pair of flexurejoints 22A and 22B and because the bending axis of the second pair offlexure joints 15A and 15B is coincident with the Y axis. The gimbalmember 28 will remain stationary however because the bending axis of thefirst pair of joints 14A and 14B is aligned with the X axis rather thanthe Y axis. The outer mounting member 27 will be permitted to rotateabout the Y axis with respect to the stationary gimbal member 28 becausethe bending axis of the third pair of joints 21A and 21B is coincidentwith the Y axis. Accordingly, it is believed apparent that the flexuresuspension assembly of the invention has two degrees of angularrotational freedom about the X and Y axes and that the entire assemblymay be rotated about the spin axis Z. Since the bending axes of the fourpairs of flexure joints are aligned with either the X axis or the Yaxis, the suspension assembly prevents translatory movement of the outermounting member 27 with respect to the inner mounting member 26 alongall three of the X, Y and Z axes.

As mentioned previously, two of the axially extending threaded holes 24are provided in each of the gimbal members 28 and 29. Each of theseapertures is adapted to receive one or more of the threaded cylindricalbalance weights 60 which are shown in FIG. 5 of the drawings. Eachbalance weight may be screwed into the threaded aperture associated withthat weight to a desired distance by means of the slot 61 formed in oneend of the weight. The apertures 24 and threaded balance weights 60combine to provide a means of adjusting the moment of inertia of each ofthe gimbal members 28 and 29. Since the moment of inertia of a rotatingmember depends upon the mass of the member and the distance from theaxis of rotation of the mass, the moment of inertia could be adjusted bychanging either or both of these variables. The threaded apertures 24 ofeach gimbal member are disposed in the central portion of the gimbalmember and extend through the arm portions of the member which lie oneither side of the spin axis Z. Accordingly, the threaded balanceweights 60 could be made in different weights to control the mass of thegimbal member and may also be threadedly inserted into the apertures 24to different points along the axial length of the apertures to controlthe distance between the mass of the gimbal member and its axis ofrotation Z. This moment of inertia adjusting arrangement permits thegimbal member inertias to be tuned to reduce or eliminate any flexurerestraints imposed upon gyroscope operation by the flexure suspensionassembly. The 90° displacement of the gimbal members with respect toeach other and the provision for inertial tuning permits the eliminationof rectified error torques associated with angular and linear vibrationswhich occur at twice the flywheel spin speed. The adjustment isgenerally made for a predetermined spin speed.

The flexure suspension assembly of the invention is structurally strongand provides good radial and axial support without the imposition ofsubstantial flexural restraints. Since the flexure joints arealternately positioned with respect to the flywheel, the flywheel isessentially supported radially by two radial flexure joints loaded intension and two axial flexure joints loaded in shear. For example, asthe inner mounting member 26 is rotated by the gyroscope spin shaftabout the Z axis, the axial flexure joints 14A and 14B will be loaded inshear and the radial flexure joints 21A and 21B will be loaded intension. Similarly, the axial joints 15A and 15B of the second gimbalmember 29 will be loaded in shear and the radial flexure joints 22A and22B will be loaded in tension. Axial support is provided by the fouraxial flexure joints 14A, 14B, 15A and 15B which are loaded in tensionand by the four radial flexure joints 21A, 21B, 22A and 22B which areloaded in double bending. The good radial support provided by theflexure suspension assembly of the invention means that the stiffness ofthe flexure joints may be kept to a minimum, thereby minimizing theflexural restraints imposed upon gyroscope operation by the suspensionassembly. Since the flexure joints 21A, 21B, 22A and 22B are loaded intension under a radial load, they can utilize the excellent tensionstrength of steel and other materials and can be made with lessstiffness and with a much lower flexural restraint than a flexure jointof comparable strength which is loaded in shear or double bending. Thereduced flexural restraints reduces errors in gyroscope operationarising from spurious error torques and simplifies the tuning of thegimbal member inertias. Additionally, the method of the invention formaking flexure suspension assemblies may be easily practiced withoutexcessive handling of delicate parts since separation of the twocylindrical members 10 and 11 into the parts of the assembly is notcarried out until after these two members are joined together.Consequently, the delicate flexure joints are protected from damageinherent in prior art methods where the individual cylinders areseparated into component parts prior to joining. Finally, the innermounting member 26 may be centrally mounted to the gyroscope spin shaftso that the flywheel inertial load is evenly supported at the shaftmounting surface. The large surface area provided by the end 34 of theinner mounting member 26 may be joined directly to the end of thegyroscope spin shaft.

It is believed apparent that many changes could be made in theconstruction and described uses of the foregoing flexure suspensionassembly and many seemingly different embodiments of the invention couldbe constructed without departing from the scope thereof. For example,the particular configuration of the gimbal members and inner and outermounting members could be varied to suit a particular application.Additionally, the suspension assembly could be utilized in single axisgyroscopes or other types of inertial devices having a flywheel andrequiring at least one degree of angular rotational freedom.Accordingly, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

What is claimed is:
 1. The method of making a flexure suspensionassembly having two degrees of angular rotational freedom about firstand second axes which are perpendicular to each other and to a referenceaxis comprising the steps offorming first and second pairs of radiallydisposed single axis flexure joints, having bending and longitudinalaxes, in a first cylindrical member, the flexure joints of each pairbeing disposed on opposite sides of said first member with the bendingaxes thereof in axial alignment and the longitudinal axes thereofsubstantially parallel to the longitudinal axis of said first member,the bending axes of said first and second pairs of joints beingorthogonally related to the longitudinal axis of said first member;forming third and fourth pairs of radially disposed single axis flexurejoints, having bending and longitudinal axes, in a second cylindricalmember having a central concentrically disposed aperture therein adaptedto receive said first member, the flexure joints of each of said thirdand fourth pairs being disposed on opposite sides of said centralaperture with the bending axes thereof in axial alignment and thelongitudinal axes thereof substantially perpendicular to thelongitudinal axis of said second member, the bending axes of said thirdand fourth pairs of joints being orthogonally related to thelongitudinal axis of said second member; joining said first member tosaid second member with said first member concentrically disposed in thecentral aperture of said second member to form a cylindricalintegrally-connected composite member having a longitudinal axiscoincident with said reference axis and the bending axes of said firstand fourth pairs of flexure joints coincident with said first axis andthe bending axes of said second and third pairs of flexure jointscoincident with said second axis; and separating said composite memberintoa cylindrical inner mounting member having the longitudinal axisthereof coincident with said reference axis, an annular outer mountingmember concentrically disposed about said inner mounting member andseparated therefrom by an annular section of said composite member, afirst gimbal member comprising a first segment of said composite memberannular section coupled by said first pair of flexure joints to saidinner mounting member and by said third pair of flexure joints to saidouter mounting member, and a second gimbal member comprising a secondsegment of said composite member annular section coupled by said secondpair of flexure joints to said inner mounting member and by said fourthpair of flexure joints to said outer mounting member, so that relativeangular rotation between said inner and outer mounting members ispermitted about said first and second axes.
 2. The method of making aflexure suspension assembly as claimed in claim 1 whereineach flexurejoint of said first and second pairs of flexure joints is formed byboring a pair of radially disposed, closely spaced and radiallyseparated holes in said first cylindrical member, and each flexure jointof said third and fourth pairs of flexure joints is formed by boring apair of radially disposed, closely spaced and radially aligned holes insaid second cylindrical member.
 3. The method of making a flexuresuspension assembly as claimed in claim 2 wherein said first and secondcylindrical members are joined by cementing them together.
 4. The methodof making a flexure suspension assembly as claimed in claim 2whereineach of said gimbal members is a bifurcated member having twoparallel arm portions disposed on opposite sides of said inner mountingmember and interconnected by a central portion at one end of the endsthereof, and said gimbal member central portions are radially disposedat opposite ends of said inner mounting member and substantiallyperpendicular to each other, so that said gimbal member arm portions areinterleaved in quadrantal relationship about said inner mounting member.5. The method of making a flexure suspension assembly as claimed inclaim 4 whereinsaid first and second pairs of flexure joints areconnected between said inner mounting member and the central portions ofsaid gimbal members, and said third and fourth pairs of flexure jointsare connected between said outer mounting member and the arm portions ofsaid gimbal members.
 6. The method of making a flexure suspensionassembly as claimed in claim 5 further comprising the steps offorming athreaded aperture in each of said gimbal member central portions, andinserting threaded balance weights in said threaded apertures to adjustthe moment of inertia of said gimbal members when the flexure suspensionassembly is rotated about the reference axis thereof.